The invention relates to a method for the production of a glow plug of the type having a housing, a ceramic glow pin and a protective tube from which a section of the glow pin projects, with said section leading to a glow tip and being thinner than a thicker section arranged in the protective tube. Such glow plugs are generally known from DE 10 2009 048 643 A1.
Ceramic glow pins are fragile. Glow plugs with ceramic glow pins therefore usually have a protective tube in which the glow pin is placed. Such a protective tube can protect the glow pin from damage over the majority of its length and thus reduce the risk of a glow pin breaking. In order to prevent a piece of the glow pin from falling into the combustion chamber of an engine in the case of a glow pin breakage, it is known from DE 10 2009 048 643 A1 to crimp and thus constrict the protective tube at its front end after placing onto the glow pin. This protective tube surrounds a glow pin, the diameter of which increases behind the crimped end region of the protective tube. If the glow pin breaks in the protective tube, a falling out of a broken glow pin piece can thus be prevented.
The glow pin diameter inside the protective tube can change only by some tenths of a millimeter. This is a problem because the glow pin must not be stressed while the protective tube is compressed. Moreover, by compressing, the protective tube is deformed not only plastically but also to some extent elastically. The elastic deformation is not maintained, so that the protective tube re-expands after compressing. It is therefore hard to ensure that the protective tube remains constricted at its end to such an extent that the glow pin is secured in the protective tube.
From EP 1 239 222 A2 it is known to solder the glow pin into the protective tube and to thus secure it from falling out. A problem here is that during the cooling of the solder, tensions occur which can lead to crack formation in the glow pin.